Re: How I Met Your Mother: Barney and... (Spoilers ahead...)
There is a Slapbet Countdown
website allegedly counting down to the next slap, placing it on Monday, May 6th, near the end of the episode. Whether this is correct or not, who can say - but the domain *is* owned by 20th Century Fox.
Yeah, that site has been around since before Slapsgiving. They reset it after every slap.
It was even included in the episode; Marshall directed Barney to the website.
Several other HIMYM websites that are real:
~Tighr™: Not helping the situation since 1983